This invention relates to a magnetic recording medium, and more particularly, to an improvement in the durability of a magnetic recording medium of the hard type such as magnetic disks and drums.
Magnetic recording media used in cooperation with magnetic disk apparatus are generally known as magnetic disks or disk media and have the basic structure comprising an annular substrate having a magnetic layer usually on each of its surfaces.
The materials of which the substrates of such magnetic recording media are made include two types, hard materials such as aluminum alloy and plastic materials such as Mylar as also used in magnetic tape media. In general, the former is called a magnetic disk of the hard type and the latter a flexible disk.
The magnetic recording media for use with magnetic disk or drum apparatus, particularly hard type magnetic disks encounter some problems of durability and abrasion resistance against mechanical contact with a magnetic head. To this end, magnetic recording media are usually provided with a protective coat. Known as the protective coat of such media are protective films of inorganic material and lubricating films of solid lubricant.
The inorganic protective films used in the prior art are formed from, for example, Rh and Cr as disclosed in Japanese Patent Publication No. 52-18001, Ni-P as disclosed in Japanese Patent Publication No. 54-33726, Re, Os, Ru, Ag, Au, Cu, Pt and Pd as disclosed in Japanese Patent Publication No. 57-6177, and Ni-Cr as disclosed in Japanese Patent Publication No. 57-17292. The commonly used solid lubricants are inorganic and organic lubricants including silicon compounds such as SiO.sub.2, SiO, and Si.sub.3 N.sub.4 as disclosed in Japanese Patent Publication No. 54-33726, polysilicic acid and silane coupling agents such as tetrahydroxysilane and polyaminosilane as disclosed in Japanese Patent Publication No. 59-39809, and carbon.
The conventional protective films formed on the magnetic layer from these materials are somewhat unsuccessful in enhancing the durability, abrasion resistance, weatherability, and corrosion resistance of the associated media and suffer from the phenomenon called grip that the head adheres to the medium surface.
In our copending application Ser. No. 943,329 filed Dec. 19, 1986, we proposed a combination of a topcoat layer and a protective carbon film on a magnetic recording medium, the topcoat layer comprised of an organic fluorine compound of the same type as used in the present invention and characterized by improvements in durability, abrasion resistance, weatherability, corrosion resistance and grip resistance. In our copending application Ser. No. 033,617 filed Apr. 3, 1987, directed to a similar magnetic recording medium, the topcoat layer is formed from an organic fluorine compound by gas phase deposition.
Also, in our copending application Ser. No. 868,511 filed May 30, 1986, we proposed a topcoat layer for a magnetic tape having a metal magnetic thin film layer, the topcoat layer being formed from a fluorocarbon resin by sputtering or ion plating.
In general, the disk medium has the structure wherein various necessary layers including primary, magnetic, and intermediate layers are disposed one on top of the other on a substrate. The durability of medium having such a layered structure depends on not only the nature of a protective layer disposed on the top surface of the medium, but also the adhesion or bond strength between the respective layers. A defective bond between any two layers will lead to a loss of the overall medium durability. There is the need for further improving the overall durability of magnetic recording medium.